1. Field of the Invention
The present invention relates to a distillation column reactor used to concurrently carry out chemical reactions and separate the reactants from the reaction products by fractional distillation- More particularly the invention relates to special trays used within the distillation column reactor and their arrangement therein. Most particularly the invention relates to a tray which comprises a catalyst support plate having vapor openings and a draft chimney above the support plate to provide better contact and mixing.
2. Related Art
The advantages of combining the chemical unit operations of distillation and catalysis in one apparatus are well recognized. Catalytic distillation, as the combination is sometimes called, may be applicable foremost to certain chemical systems in which a desirable reaction that is limited by the chemical equilibrium proceeds in a temperature and pressure regime, in which livid and vapor phases co-exist, and in which the separation of the reaction products from the reactant(s) is required.
The advantages of catalytic distillation include the possible utilization of any heat of reaction in the distillation, the removal of the reaction products from the reaction zone immediately after formation, the return of the unreacted reactants by distillation to the catalyst zone and thus the opportunity to achieve most nearly complete conversion of the reactants.
Various concepts have been employed and proposed for the effective combination of catalysis and distillation in a single vessel. Most provide for the location of one or more fixed beds of catalyst in the reaction zone of the apparatus.
Where the catalyst is used as distillation packing, it is may be contained in cloth belt or wire mesh baskets. Additionally U.S. Pat. Nos. 4,443,559 and 4,215,011 disclose a particulate resin catalyst contained in pockets on a cloth belt. The cloth belt is arranged and supported in the column by wire mesh intimately associated with the cloth pockets. U.S. Pat. Nos. 4,439,350 and 4,536,373 disclose apparatus for placing the cloth belts containing the catalyst on conventional distillation column trays. In one commercially proven process, the catalyst is contained in pockets sewn into a fiber glass cloth which is then rolled into a bale, which serves as a distillation structure. Multiple bales are located on support trays inside a distillation tower.
This use of a catalytic distillation column reactor lends itself particularly well for reversible reactions in the liquid phase. See for example U.S. Pat. Nos. 4,336,407 (etherification), 4,482,775 (isomerization), 4,242,530 (separation of isobutene from C.sub.4 streams) and 4,551,567 (deetherification). The combination is useful because the reactants, in the liquid phase are quickly separated from the reaction products due to boiling point differences by fractional distillation. Thus the reverse reaction is suppressed.
The performance of catalytic distillation systems utilizing heterogeneous catalysts is highly dependent on the arrangement of the catalyst beds in the distillation column. The processes taking place in the catalyst zone represent a highly complex physicochemical system. Reactions approaching the chemical equilibrium between the reactants and the reaction products will occur. There will also take place mass and heat transfer between the liquid and vapor phases leading to an approach to the physical phase equilibrium. The mass and heat transfer and thus the phase equilibrium will be influenced by the heat of reaction.
In many chemical reactions involving organic compounds the catalyst is deactivated over a period of time which may be as short as a few days or as long as a year or more. The cause may be the deposition of polymers on the catalyst surface, the neutralization of acid sites on ion exchange resins or some other mechanism. Invariably such catalyst deactivation requires either replacement or regeneration of the catalyst. More often than not, replacement or regeneration entails considerable expense and requires a shutdown of the entire system resulting in a loss of production.
Several different arrangements have been disclosed to carry out catalytic distillations. For example British Patents 2,096,603 and 2,096,604 disclose placing the catalyst on conventional trays within a distillation column. A series of U.S. patents, including those listed above discloses using the catalyst as part of the packing in a packed distillation column. More particularly U.S. Pat. Nos. 4,443,559 and 4,215,011 exemplify the latter.
Fluidization of the catalyst on the trays by the action of the vapor passing through the tray has also been suggested as in U.S. Pat. No. 4,471,154, wherein a fluidized height of the bed is determined, at least in part by the volume of the bed defined by the tray containing the catalyst and a screen, i.e., about 2 to 10 times the height of the settled catalyst bed.
Since most reactions occur in the liquid phase and vapor flow through the catalyst on trays may cause problems such as increased pressure drop and catalyst attrition, vapor by-passes around the catalyst containing trays have been proposed. See for example U.S. Pat. Nos. 4,847,430 and 4,847,431. Disclosed therein are alternating catalyst containing trays and standard distillation trays with the vapor from the distillation trays by-passing the catalyst containing trays and passing directly to the next higher distillation tray (U.S. Pat. No. 4,089,752 discloses the by-pass in a non-catalytic reaction distillation system).